


Punnilingus

by uttermost_Oops



Category: Undertale (Video Game)
Genre: Cunnilingus, Ecto-Genitalia (Undertale), Ecto-Tongue (Undertale), Ecto-Vagina (Undertale), Fontcest, Incest, M/M, One Shot, Oral Sex, Sibling Incest, Top Papyrus, bottom sans
Language: English
Status: Completed
Published: 2018-04-16
Updated: 2018-04-16
Packaged: 2019-04-23 12:18:22
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,276
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/14332320
Author URL: https://archiveofourown.org/users/uttermost_Oops/pseuds/uttermost_Oops
Summary: Papyrus has something new to show Sans.Sans wants to know more.





	Punnilingus

It starts with a complete and total accident.

The first time Papyrus conjures up a bright orange tongue, he runs, long limbs propelling him forward, all the way home to show his big brother. When he gets there and it lolls out of the side of his mouth, Papyrus’ eye sockets practically glowing with pride as his hands clasp eagerly in front of him, Sans is amazed by how... long it is. Everything about Papyrus was grand and larger than life—he’d somehow ended up taller even though he was younger, his HP was better, his zest for being alive every day was far more apparent, and even one of his attacks stretched the boundaries of another monster’s limits should they last long enough to see it. So could Sans really have expected anything less?

Sans’ gaze is fixed, not on the actual tongue itself, but rather the orange glow it casts upwards across Papyrus’ features as he offers the sight of it to him. At first, Sans just stares. He uncertainly raises both hands and while he does so, Papyrus’ grin widens a little like he’s excitedly granting his brother permission to take a better look. Carefully cupping Papyrus’ jawbone between his hands, Sans inspects the new appendage, taking his time and gently pivoting Papyrus’ face side to side. He cradles his skull like it’s a treasure box encasing a precious, deep citrine jewel, and Papyrus is happy enough to stay as still as he can for once, his trembling body overcome with joy while his older brother looks over he and his new body part. And then he stiffens when he feels a bony digit slowly slip up the fleshy side of his tongue.

Papyrus’ breath hitches, the skeleton frozen and unsure of what to do. It… is just magic, after all, and Sans is probably just curious, never having seen anything like it before. So when Sans asks, “Is this okay?”, his thumb barely pressing into the soft bed of magic in his mouth, a flood of relief washes over Papyrus and he smiles and nods, taking care not to disturb the finger on his tongue. The corner of Sans’ mouth upturns just a hair and he picks up where he left off: stroking this new conjuration sitting in Papyrus’ jaw, running the pad of his thumb along the surface at first and then, after a particularly interesting thought, putting his index finger in the center and running it up and down the dip in the middle.

By now, Papyrus’ expression visibly changes. A tingly warmth spreads across his cheekbones, but he does his best not to let it show. He really shouldn’t be getting turned on by his older brother checking out his new magic, he always showed Sans first when he came up with something new... But the intense look in Sans’ eyes as they bore straight to his gaping mouth, that bony finger of his running slow, thin stripes along his tongue while his other hand at Papyrus’ jaw keeps his skull from moving, has Papyrus only hoping that Sans isn’t noticing the way he’s struggling not to pant.

After being allowed his hands-on closer look, Sans just can’t believe how soft it is—the magic forming their naturally dense, bony bodies must be something inherent and automatic as opposed to this soft conjuration, and the only other magic either of them had summoned before had been other bone-like things or bursts of attack arcana. But this… Sans’ eyes close just a touch, half-shut as he watches his obedient little brother let him tease his mouth with his finger.

This is entirely new. And Sans wants to know more.

//

The second time it happens, the two skeleton brothers are more frustrated than anything.

Sans sits facing his brother in Papyrus’ lap as they settle for the night on their couch, their pelvises practically shoved up against one another and their leg bones tangled in a bit of a heap. Sans claims it was to get a “better look”, to get a firsthand view of the blend of science and magic he hopes to witness, but Papyrus has a deep, unspoken suspicion that perhaps there was a little something more driving that decision.

For a while, nothing happens. They just try, together, to figure out what it is that gives Papyrus this magic; this soft little jewel-toned accessory that isn’t like the rest of his body? Sans taps his chin as he turns thought after thought over in his mind, and Papyrus does the same, his torso bent at a slight angle to better match his brother’s height.

“OOH!” he quips. “Maybe try hurting me? I bet if we engage in a fight, the magic will surface! That’s how monsters battle, after all...”

“Sure, but...” Sans gets what he’s saying and curls one of his fingers behind his thumb, giving a half-hearted flick to Papyrus’ forearm. “The intent isn’t there.” Papyrus knows Sans would never hurt him, and would never want to do so, either. They scrap that idea and continue their thoughtful humming, stumped by this dilemma while they hypothesize back and forth for a few hours.

What if I? No, no. That won’t do. Maybe if you? Nope. Nothin’. Ooh, what if we tried? Huh-uh.

It wouldn’t be until a few days later of repeating this routine, Sans in Papyrus’ lap as they spend their nights on the couch, that they realize the intent to hurt isn’t necessary to invoke this new magic—but rather the opposite.

Sans makes the discovery first.

If the intent to harm is what triggers someone into activating their battle magic, magic that was hard and powerful and meant to protect, to attack, then of course? Wouldn’t it make sense that the intent to please would help conjure up magic that was soft and tender, meant to enjoy and savor?

With his thumb, Sans strokes a line across the ridge of Papyrus’ lower jaw and watches his reaction when he does it a second, a third time. Papyrus is unusually quiet, although eager to let his smart older brother take the lead for once. Sans’ expression is focused and intense, yet gentle as the tip of his thumb carefully moves over the bumps of Papyrus’ bottom teeth and parts his mouth. There is no shimmering, brilliant orange glow behind them yet, but Sans is determined. The palm of his hand snakes its way back across Papyrus’ jaw to run down his neck, caressing the sides of his ribs and skimming down the circumference of his spine, and he swears on his 1-hp life that Papyrus actually shudders under his touch.

This is a good thing, Sans tells himself, even if his breath is a little shaky. He has to believe it’s a good thing, that it’s something he’s doing to learn—how else will they figure out this new magic? How else will they know what to do to make it happen again? And again? He grits his teeth and tells himself that’s all they’re doing. Learning.

“Well,” he coughs, finally interrupting the quiet of the room after getting nowhere for some time. “What were you doing when it first showed up?” His face looms closer and closer to the inside of Papyrus’ jaw as it hangs open, craning as he peers into the dark shadows inside.

“Um!” Papyrus answers with a little difficulty, Sans’ hands still on and in his face. “I was! Hanging out with Undyne, and... she said a rather terrible pun, but because it was terrible it was actually pretty good! So it made me laugh and. I.” His jaw swings shut then, teeth clicking together. Sans leans back, reflexively pulling his hands with him. “Thought of you.” Sans tilts his head as he looks forward at Papyrus, whose gaze won’t meet his. It’s only quiet for a moment before Papyrus smiles and turns back towards his brother so he can gleefully quip, “And then it showed up! Just like that.”

“I see...” Sans stays still for a minute.

If he had a lower lip to bite, he would. And he’s not really sure why he has that desire now; he’d seen plenty of people do it for tons of reasons—Alphys did it when she was nervous, Undyne did it when she was mad, even the human had done it from time to time when they were deep in thought over the solution of a puzzle. So what’s this feeling he has now?

He sighs.

His fingertips start to graze along the top curves of Papyrus’ pelvis, and he offers a smile. If he’s careful, he can feel Papyrus shift a bit beneath the touch.

“Hey Paps, what would you call the king of rock and roll if he were a skeleton like us?”

Papyrus’ head turns just a fraction, eyes squinting almost as if to say don’t you dare.

“Pelvis Presley.”

Papyrus gives a short laugh, but he doesn’t wanna give Sans the satisfaction of a job well pun.

Sans’ smile brightens anyway as his hand drags upwards, doing what he can to ignore Papyrus’ body moving with him, almost arching against his touch. His browbone furrows just a hair. Papyrus... Does not make things easy. When his palms are brushing over Papyrus’ ribs, the tips of his fingers grazing over the slightly softer cartilage in the sensitive spots, he pauses.

“Hey Paps.”

His smile is met with one of his favorite looks. Is there a word for a blend of obvious annoyance, yet reluctant amusement? “Nyes, brother?”

“What do you call it,” Sans says, watching his own fingers caress over the bones there a little bit slower than what was probably appropriate, “when a skeleton helps advance something along…?”

“…”

“A cont-RIB-ution.” His fingers ever so slightly dip into the hollow spaces between three or four of Papyrus’ ribs, careful not to hurt him while his body finally shakes with laughter.

Between chuckles, Papyrus says, “Now that’s what I call a rib tickler if I do say so myself!” He laughs a little harder at his own joke and brings his hand up to snicker behind it as his face scrunches in amusement. Sans’ shoulders shake a little, too, as he laughs behind his teeth. He watches happily: this is another of Sans’ favorite looks, when Papyrus is caught off guard by his shitty puns and finally rewards him with a good audience.

Sans’ smile falls a little and he swallows down the lump in his throat, the lump he’s not sure even really exists since he doesn’t have an esophagus. His exhale is a little labored this time, and maybe if Papyrus looks a little closer he might see a couple of beads of sweat starting to form, but Sans shakes it off and says, “What do you call a skeleton… realizing his feelings for another skeleton?” His pupils move to the window behind them and the quiet world of Snowdin calming down for their bastardized version of “night” greets him. There is no sun, and there is no sunset, and technically, there is no night, either, but there is a designated portion of the day dedicated to settling down and sleeping and being calm, and this is it.

Like the rest of the world, Papyrus is quiet, eyes a little wider, a little more attentive than usual as he stares up at Sans. “Hmm...?” His hands curl almost awkwardly in front of himself, like he’s waiting to hear… news. And he’s not sure if what he’s anticipating is good or bad.

Sans stares at the various citizens returning to their homes, dimming their lights and locking up as he mirrors Papyrus’ quiet for a minute. Maybe a small, cowardly part of him just wants to preserve this moment, a moment where he knows everything is still safe and unchanged. A moment that he hasn’t fucked up yet. A moment that he knows he might wish he had held onto just a little longer, a moment he hopes doesn’t lead into another moment that he will regret deeply.

So when there’s nothing left to watch but the solemn white powder of bright snow and the silent faces of buildings long since emptied to meet his gaze, he chuckles once, a little bitterly. This stupid joke would work so much better if there was a sun, and if the sun was setting like he knows it does on the surface, and if there was night. But whatever. He’s used to rolling with the punches—or maybe just dodging them entirely. Two white pinpricks of light shift direction from the glass to his younger brother’s stare, Sans’ face inches from Papyrus’ as he finalizes his decision.

“A shot in the dark.”

And then he closes his eyes as their teeth clink against one another’s, and they kiss, a hush as gentle as Sans’ palms wrapping around Papyrus’ upper arms cocooning them.

In the darkness of the room, the seed of an orange glow suddenly swells and then beams between their mouths, Papyrus making no attempt to move away while orange light illuminates the two skeletons.

//

When it’s Sans’ turn to finally do some conjuring, it’s entirely intentional.

The way Papyrus’ tongue is all over him has him breathing hard, and Sans is surprised by how WET it is. He knew his own body could “emit slime”, as it were, no problem—he was always sweating for one reason or another and on the occasion of the rare sick burn he found himself letting out a monsterly tear or two, but this? This new, long, soft, wet, jewel-toned tongue that Papyrus had apparently mastered in his spare time was nothing but surprise after surprise to Sans.

Papyrus’ arms snake underneath Sans’ thighs, his hands gently but firmly clasping around his wrists to keep them at his sides while he lays back. His shoulders separate Sans’ legs, that tongue of his making friends with some magic of Sans’ own design—a plump, sapphire pussy, all for his little bro. And in this moment, hotly staring down at his younger brother, Sans is wishing he too could conjure up a tongue; wants it to loll out of the side of his mouth while Papyrus literally works his magic, but it takes so much energy already just to keep his new pussy in place that it’s a relief, really, when Papyrus tells him leave it to me! It is, after all, orange magic that’s all about movement and blue magic that’s all about staying still, is it not? And just as Sans is about to remind him that’s not how it wo—oh. _Oh_ … _ahhn_...

And suddenly, Papyrus’ magic, wet tongue is licking a stripe between Sans’ slightly parted lips, caressing the silky insides. Sans pants, surprised when the wet of Papyrus’ fleshy tongue and Sans’ honeyed pussy meet. The melding of their new body parts is creamy and supple and wet and sends tingles of electricity up his spine which shuts Sans up so fast it’s not even funny.

Papyrus raises his head so he can get a better look at his brother, and he’s able to lift his skull long before the appendage actually parts from Sans’ lips, it’s so long. Then he says, “Hey Sans? Did you know that your—u-uh…” he pauses, a blush dusting his cheekbones. How can he be in this position, eating his brother out, and not just say it? “—bits, here, taste like… candy?”

Sans exhales hotly, a breath he didn’t know he was holding. One of his eyes are shut halfway, and he looks down past his exposed body into Papyrus’ curious expression. Though his voice is almost dull, he knows he’ll get a good reaction, so he offers Papyrus a weak smile. “You tellin’ me I got a flavored skeleton pussy?”

“gjkhdkghdkjhsa!!!”

Sans’ head tilts, brow a bit furrowed as he’s almost distracted by the impossible feat only his brother could accomplish. “How…” Keysmashes? In dialogue? “How did you do that?” But his face softens again, muttering a single, quiet, “Oh,” when Papyrus ignores him and gets back to work. His head dips low and his long tongue squelches as it drags along Sans’ newly wet lips, tracing impossible ribbons of circles all along the outside.

“Fuuuh…” Sans’ fingers dig into the sheets beneath them, his body arching up towards the ceiling even though Papyrus still isn’t letting him move. “ _…uck_ , Papyrus…” Sans grits his teeth, pupils unable to focus on anything as they waver in his sockets.

“Nyeh heh…”

A tiny smile graces Papyrus’ mouth, even if it’s squished up against his brother; he kinda likes it when Sans loses his cool like this. He lets go of Sans’ wrists, a courtesy so that his brother’s hands don’t tremble so much as they seek purchase somewhere on the bed. His tongue is so long, it’s kind of folding in on itself as he goes, but it’s prehensile enough to allow for a really good time.

“Ah… hah, nnmm.” Sans’ quiet little moans fill the room and it makes Papyrus’ eyes shut a bit as they lower, staring at the subtle cyan glow of Sans’ crystal pussy, which tastes like… what does it taste like? Magic taste buds lapping at even more magical pussy was… quite something. Very different from the magic of monster food turning into pure energy when they ate. But if he had to put a name to it, he might be inspired by “blue raspberry”. And honestly… it’s the single most tasty treat he’s ever had in his mouth.

Not only is Sans’ sugary-sweet pussy delicious, but it feels good against Papyrus’ tongue, too. The way Sans’ lips stretch and pull at him, the way the inside of the jelly-like slit massages the flat surface, sending shivers down his own spine, has him sweating for more, too. It feels good, a tongue feels just as good, and he can feel heat spreading in his jaw, his chest, and everything tingles just a little. His head veers up and down as he slips his tongue in and out of the shallowest parts of Sans’ magic like an eel, the magic accessory sometimes seemingly moving of its own free will.

Only the sounds of Sans’ shallow breathing and the suckling of their soaked appendages fills the room.

Papyrus captures Sans’ trembling thighs between the bent V of his arms, sandwiching them there in the crook as he shifts his hips up a little to get a better angle. Sans’ voice cries out once, strained by the new sensation almost like he’s in pain from all the attention, but Papyrus knows better than to stop—if he really wanted to, Sans would tell him when he’s had enough, but for now his older brother seems happy to let him do whatever he wants until further notice.

Leaning forward, Papyrus lets his teeth just barely scrape along the peachy mound of Sans’ lips as his tongue traces an S all around and outside his pussy, over and over, and then without warning it delves inside. From in front of him, he can hear his brother choke off a sharp inhale and Sans’ eyes are wide open, though trembling as they pierce through the dark nothingness in the shadows of their ceiling.

A few huffs of fragmented air escaping from his mouth later and the beads of Sans’ white pupils move down to stare wide-eyed at his brother. Squeezed tight by the walls of his magic sapphire pussy, Papyrus’ tongue thrusts in and out all the while without breaking eye contact. Papyrus stares intently back at Sans, and it’s almost like a game, watching Sans’ chest heave up and down, even without lungs. But then the look in Papyrus’ eyes shifts ever so slightly, shutting just a little bit as the clash of glowing orange and blue cast mixed light on his face, and Sans’ expression softens again. His mouth opens, making audible all the hot air of his heavy breathing, and his voice gets desperate.

“Hhhah, god… Papyrus…” Sans moans, his body sinking into the bed under the weight of his exhaustion as Papyrus laps at him. His pussy and his brother’s tongue are both thirsty for each other, the magic nearly melting together and pulling and pushing against one another which sends little trickles of electricity all the way down to the tips of their toes. “Hhhh... Please...”

Sans’ fingers curl up stiffly to his side and his chest tightens, eyes squeezing shut. He’s gonna die, he’s gonna die, he’s _really_ gonna… Shouldn’t they have thought about how if even just a little too much pain could kill him, who knew what a whole lotta pleasure could do? But then he feels Papyrus’ arms release his thighs and two long-fingered hands slide forward on the bedsheets to intertwine with Sans’. Though his legs suddenly clamp down with two guilty clicks on Papyrus’ skull, he’s grateful for the contact: Papyrus is here, gazing at him with a blend of love and lust in his eyes even if Sans can’t see for himself, and that’s all that matters.

Papyrus hears the muttering under Sans’ breath getting louder and louder with each lewd splash of his tongue. “Mmmn… haaa… fuck, h-ha…” Sans’ eyes close and his smile stretches across his face as ecstasy completely absorbs him. “Hhhaaahn, shit…! Aha!” He laughs, teeth gritting as his moans grow more guttural and needy, and it excites Papyrus to hear such nasty noises coming from him. Though he doesn’t currently have anything summoned between his own legs, a blazing heat still builds in his pelvis in tandem with the strokes of his tongue and he lets himself start chasing his own high.

Sans’ hands shake in Papyrus’ grasp; shake him off, letting him know to let go, and suddenly they’re digging into the top of his skull as he throws his own head back into the pillows. He practically shouts out various grunts, curses, and directions, his hips rolling against Papyrus’ mouth as his hands guide his skull to go a little faster, a little harder, a little deeper.

“Heh… hehn…” Papyrus mutters, muffled against the gelatinous pussy. At least now that his hands are free, he can try something…

The long bones of one of his arms curl around one of Sans’ thighbones again and he digs his thumb into the little pearl at the top of the magic folds, swiping over his clit a few times. It’s almost a little difficult to do skillfully with Sans’ overwhelming bucking, but the fingers of Papyrus’ free hand encircle the circumference of one of Sans’ thighs easily and he manages to hold him in place. They’d agreed to leave it to Papyrus, after all, hadn’t they?

“Ugggghn, shit!” Sans’ body curls inward a little then, his pussy pressing as desperately as it can against the source of its pleasure for more, more, more. “Pap, I’m, gonna… I’m gonna,” he groans breathlessly, tightness flooding over his body one last time.

Without removing his tongue, Papyrus forcibly nuzzles the side of his head into Sans’ hips as a bright heat encompasses his body, bursting in his chest and his hips as he comes, too. His cries aren’t as loud as Sans’, which are rather guttural and short, but he does muffle out a groan between those magic lips of his brother’s and he can’t help but smile as both their heads go blank in pure bliss for a minute.

Sans grunts again when Papyrus finally tugs his tongue out, out of his brother and back into his own mouth. To his surprise, a pool of translucent (and deliciously sweet, blue raspberry-y) liquid spills out along with it and he perks up, poking at the entrance and pulling one of the lips to the side with a curious finger. Sans is too tired to protest, but he blearily looks up with a smile on his face.

“Oh!” Papyrus says, delighted to be the one to do the magic-inspecting now. A couple drops of goo leak from the fleshy slit, glowing just as brightly as the rest of their magic. “It appears to be… self-lubricating?” He stabs a finger into one of the droplets on the sheet, hoping any stain that might form will come out with a good wash. He sighs, knowing he’ll have to start learning how to combat ecto-ejaculation.

Sans chuckles. “Yeah, they do that.” Though he’d browsed through plenty of anatomy books and underground afterdark sites, that particular fact really nothing new to him, he supposed it was pretty cool that even temporary magic could self-regulate like their natural counterparts. And he was grateful for that, too… he could only imagine what a tongue as rough and passionate as Papyrus’ would do if there was no wet to combat the friction.

Heh… Sans’ eyes drift upwards. Maybe, though… something like that would be fun to look into…

As Sans daydreams about future possibilities, Papyrus crawls up to his side and nuzzles their cheeks together which Sans reciprocates happily. He closes his eyes and a playful grin spreads across his face. “Hey bro, I would ask if you wanna go to Grillby’s to grab a bite, but…” he opens one eye, giving his brother that trademark wink of mischief. He just can’t help himself. “I’d say you’ve had enough eating out for one night.”

“AGGGGHN!”

Sans chuckles, the orange and blue light of their dissipating magic organs fading from the room as he wraps an arm around his angrily muttering brother.

He just hopes someday he can return the favor.

**Author's Note:**

> thanks for reading! ( ´ ▽ ` )ﾉ*:･ﾟ✧


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